Conveyor dryers or ovens are often utilized where it is necessary to raise the temperature of various article to a specific temperature, and where high production rates are required. Such dryers are frequently utilized in manufacturing of screen printed shirts and other clothing articles. In order for the process to be effective, the dryer must raise the temperature of all of the thermal-setting ink on the garment to a specific temperature range in order to activate the thermal-setting process. If the garment is raised to a temperature substantially greater than the thermal-setting limit, scorching of the material and/or inks can take place. If the garment is not raised to the appropriate temperature, cross-linking of the ink will not take place.
Prior dryers have resolved the conflicting requirements of setting the ink without scorching by utilizing an extremely long heat path. Such dryers may have a heat path as long as 30 to 40 feet. By exposing the garment to the elevated temperatures for an extended period of time, by utilizing a very long heat path, acceptable production rates can be obtained at the expense of considerable energy expenditure and wasted floor space. Such dryers are also expensive to purchase and maintain.
One method used by production dryers to maintain precise temperature control is to vary the distance between the heater and the surface of the garment. Production dryers have raised or lowered the heater elements to maintain the optimum spacing. However, the movement of the heater required flexing electrical connections and an adjust mechanism within the heated chamber. These mechanisms increase the cost and reduce the reliability of the dryer.
There have been conveyor dryers that are capable of bringing a garment up to temperature much more rapidly than the long path dryers. These dryers utilize a combination of radiant heat and heated air flow. The heated air surrounds the garment to supplement the directly radiated heat and raise all portions of the inked surface to the thermal-setting temperature. Such dryers are capable of drying garments in a much shorter conveyor length, and therefore are much more energy and space efficient. However, such dryers are much more sensitive to the maintenance of exact temperatures within the heat chamber and are more sensitive to temperature fluctuations when garments are again placed on the conveyor belt after an interval where there has been an absence of garments.
It is therefore desirable to have a temperature control for conveyor dryers transfer heat to garments at an increased rate. Such a dryer would be particularly desirable where it accurately senses the actual temperature of the garment passing through the dryer and regulates the heaters and belt speed within the chamber to maintain temperatures as close as possible to an optimum set point. It is also desirable to have a temperature control for conveyors that compensates for the temperature draw down effect when the garments are reintroduced to a chamber that had been empty of garments.